9% of the population will experience a mood disorder at sometime in their lives. There are two categories of mood disorders: unipolar depression and bipolar depression. Major unipolar depression is much more likely to occur than bipolar depression (5x more likely), and is one of the most commonly diagnosed mental illnesses. Mania, the other "pole" of bipolar depression, can be experienced on by itself. The difference between people with mood disorders and "normal" people are the degree, severity, and duration of moods.

Unipolar Depression

There is a 5% lifetime risk of developing a form of unipolar depression. It is seen cross-culturally, but is diagnosed twice as often for women than as for men.

The DSM IV states that for diagnosis to be made the person must:

have a depressed mood

or have a loss of pleasure

and experience these four symptoms during the same two-week period

Emotional Symptoms

intense feelings of sadness or guilt

lack of enjoyment or pleasure in activities the individual once loved

Motivational Symptoms

Passivity

difficulty in initiating action and making a decision

Cognitive Symptoms

frequent negative thoughts

blaming oneself

low self-esteem

irrational hopelessness

Somatic Symptoms

loss of energy

restlessness

increased/decreased appetite

weight loss/gain

insomnia/hypersomnia

Some types of unipolar depression include:

Major Depressive Episodes

Dysthymia - chronic mild depression occurring over a period of at least two years, where a depressed mood and symptoms are experienced either most of the day, more days than not, or without a break of more than two months in the two year period.

Seasonal Affective Disorder - mood systematically varies with the seasonal changes of the year, often involving depression during the winter months. (if the sufferer also feels mania during the summer or other time during the year, then his or her form of SAD is classified as bipolar depression).

Mania - mood disorder of symptoms of full blown mania without periods of intense depression. The manic symptoms must last at least a week and must interfere with social and occupational functioning.

Bipolar Depression

There is a 1% chance of developing a form of bipolar depression. It is much more strongly linked to genetics than unipolar depression is.

Bipolar Depression includes the symptoms of unipolar depression followed by a period of mania, or hypomania (a shorter, less severe period of mania). The DSM IV states that a manic episode must involve

a "distinct period of abnormally and persistently elevated, expansive or irritable mood lasting at least a week"

at least three of the following symptoms

Emotional Symptoms

abnormally euphoric, elevated, or irritable mood

increased pleasure in activities

Motivational Symptoms

Increase in goal-directed activity

increase in pleasurable activities that have a high risk of painful cpnsequences

Cognitive Symptoms

inflated self-esteem or grandiosity

racing ideas or thoughts

lack of attention (easily distracted)

Somatic Symptoms

decreased need for sleep

psychomotor agitation

more talkative

rapid and pressured speech

Types of Bipolar Depression include:

Bipolar Depression

Cyclothymia - bipolar equivalent of dysthmia. Mood disorder where the sufferer has periods of mild depression followed by hypomania for more than two years.

Seasonal Affective Disorder

Theories explaining mood disorders

Cognitive Theory

Seligman’s experiments with learned helplessness in dogs led him to believe people suffering from depression: 1. blame themselves instead of the situation, 2. situation as unchangeable, 3. failure inevitable.

Similar ideas have been expressed by Aaron Beck through his cognitive triad theory about self, situation, and future. Beck believed depression is caused by errors in logic including distortions in thought processes, overgeneralization, and personalization.

Neuro-chemical theory

Depression has been linked to disruptions in the neurotransmitters norepinephrine and serotonin. This research has been strengthened by the success of some drugs in treating depression, notably the use of SSRIs to block the reuptake of serotonin in the limbic system. Lithium carbonate has been successfully used in treating bipolar depression, creating strong links to biological causes for bipolar depression as well.

Genetics

Katz and McGuffin (1993) studies using monozygotic twins estimates that about 52% of unipolar depression variance is due to genetics, while the variance is about 80% in bipolar disorder. This study suggests a very strong correlation between bipolar depression and genetics.

Environment

Depression occurs most often in women who are “working class, house bound with three or more children.” Stress and little emotional support can increase the possibility of the onset of depression. Season change correlates with the onset of depression, with more cases being reported during the winter months.

Interaction theories

Weiss and Simson’s (1985) study showed that rats exhibiting learned helplessness behavior have significant decreases in the activity of the neurotransmitter norepinephrine.